It doesn't sound stupid, just unrealistic, mainly because if you use a real guitar cab you don't have an FRFR reproduction system and an eq curve cannot force the speaker to reproduce or compensate for frequencies that it cannot handle.
IMHO is not possible. More then happy to be wrong if it is the case
I think you are 100% right regarding the frequencies handling possibilities of a guitar amp.
Anyway, could still be usefull to let the kemper "create" an EQ to try to compensate the gaps
(even if, as you said, it cannot replace a good FRFR system).